This invention relates to a process for exchanging heat between a bath requiring cooling and a station which may contain a second bath on some other device requiring heating.
More specifically, the bath requiring cooling is contemplated to be a bath in which metallic and metal-containing workpieces are surface-treated and refined as, for example, in an electrochemical process. In one such electrochemical process, galvanization, for example, a metal or metal alloy is treated by means of an aqueous electrolyte under the influence of a direct current. The speed at which the metal from the electrolyte is deposited on the surface being treated depends on the current density, which is the amperage per unit of surface area of the article being treated.
In order to obtain an optimum treatment, an essentially constant current density must be provided during the electrochemical process. The magnitude of the current density depends on the electrolyte used and on the article to be treated.
In order to obtain a sufficient current, an electrical potential must be applied. The magnitude of the potential depends on the resistance encountered by the current in the electrolyte solution. The electrical energy which must be supplied in order to overcome this resistance is converted to heat.
In some cases the heat thus generated is so great that it exceeds the capacity of the surrounding air to absorb heat at the operating temperature of the bath. In such situations the temperature of the electrolyte solution rises steadily.
In order to obtain an optimum result, however, the operating temperature of the bath must be kept within an allowable range. It is necessary, therefore, to remove the excess heat by some type of cooling mechanism.
The cooling of baths for surface treatments, for example in galvanization baths, is usually accomplished by means of heat exchangers located either inside or outside the bath. The heat is transferred to cool water, which is then discarded as waste water. This waste water might be re-used in the heated baths used to rinse electrochemically treated workpieces, but since the flow of the waste water is intermittent, this possibility is usually disregarded as impractical.
The process for cooling described above is expensive due to the rising costs for fresh water and for waste water removal. In addition, valuable thermal energy is lost.
It is also known to use cold (refrigeration) aggregates, whch raise the heat withdrawn from the electrochemical bath to a still higher level. The heat thus withdrawn is then given off to the atmosphere. This method requires the addition of further electrical energy to operate the refrigeration device. Thus, the rising cost of water is avoided but the rising cost of electrical energy must be paid and the withdrawn thermal energy is still wasted. For these reasons, the cold aggregate method not only requires a large investment but is becoming more and more uneconomical.